The present invention relates to a solid-state imaging device which employs a face-down bonding technique for mounting a solid-state imaging element, and a manufacturing method thereof.
An example of a conventional solid-state imaging device is a solid-state imaging device taught in Japanese Unexamined Patent Publication No. 204442/1994 (Tokukaihei 6-204442) (published date: Jul. 22, 1994). FIG. 11 shows a schematic structure of this solid-state imaging device, and FIG. 12 through FIG. 15 show a manufacturing method thereof.
As shown in FIG. 11, the solid-state imaging device has the structure wherein a glass substrate 101 is bonded by a conductive adhesive 106 with a solid-state imaging element 102 which has been provided with projecting electrodes 105, and a gap between the glass substrate 101 and the solid-state imaging element 102 is sealed by a sealing resin 107, leaving a light receiving area 102a. On the glass substrate 101 are formed a group of electrode terminals 103 for outputting electrical signals and a projecting frame 104 of insulating resin on and around the group of electrode terminals 103.
In the manufacturing method of the foregoing solid-state imaging device, in the first step, as shown in FIG. 12, the conductive adhesive 106 is applied by a transfer method over the projecting electrodes 105 provided on the solid-state imaging element 102.
Then, in the second step, as shown in FIG. 13(a) and FIG. 13(b), a metal film such as copper (Cu) is formed by a vapor deposition method on the glass substrate 101, and the electrode terminals 103 are formed by patterning the metal film in the form of wiring, and then the projecting frame 104 is formed by a printing method using a paste whose main ingredient is an epoxy material.
In the subsequent third step, as shown in FIG. 14, the solid-state imaging element 102 to which the conductive adhesive 106 was transferred is bonded with the glass substrate 101 having provided with the projecting frame 104 by printing the epoxy material in the second step, and heat is applied by a heating device so as to set the conductive adhesive 106 and the projecting frame 104.
Finally, in the fourth step, as shown in FIG. 15, the sealing resin 107 is allowed to penetrate to the area of a gap between the solid-state imaging element 102 and the glass substrate 101 around the outer periphery of the projecting frame 104, which is then set by heating it using a heating device.
The solid-state imaging device is used to convert the incident light on the glass substrate 101 into electrical signals by the solid-state imaging element 102 so as to output the electrical signals in the form of image signals to outside via the projecting electrodes 105 and the electrode terminals 103.
In the foregoing solid-state imaging device, when foreign objects stick to a light incident area, i.e., the light receiving area 102a, the foreign objects block the incident light and appear as black spots in the output image. Therefore, manufacture of the solid-state imaging device requires a strict measure against foreign objects for preventing adhesion of foreign objects on the light receiving area 102a. 
Specifically, such a measure can be implemented, for example, by (1) manufacturing the solid-state imaging device in a clean environment where foreign objects are strictly managed, (2) providing an additional step of removing the adhered foreign objects, or (3) by avoiding handling or operation on the light receiving surface in the manufacturing process.
However, the foregoing prior art required operation on the light receiving surface in the step of transferring the conductive adhesive 106 with respect to the projecting electrodes 105 provided on the solid-state imaging element 102, and also in the step of printing the projecting frame 104 with respect to the glass substrate 101, which posed the risk of foreign objects being stuck during the operation.
Further, the resin making up the conductive adhesive 106 and projecting frame 104 is set by heating using a heating device after mounting the solid-state imaging element 102 and the glass substrate 101 together. Thus, immediately after the transfer of the conductive adhesive 106 onto the solid-state imaging element 102 or printing the projecting frame 104 on the glass substrate 101, the conductive adhesive 106 and the projecting frame 104 have not been set yet, which prevented providing the step of removing foreign objects even when presence of the foreign objects was observed on the light receiving surface of the solid-state imaging element 102 and/or glass substrate 101, thus failing to remove the foreign objects once they stick to the light receiving surface.
Further, even though the manufacturing method of the solid-state imaging device under clean environment is applicable to the foregoing conventional solid-state imaging device, it requires a manufacturing process in a clean room where foreign objects are strictly managed, thus posing the problem of high facility cost.
Further, in the foregoing solid-state imaging device, because the metal film is formed directly at the interface with the glass substrate 101, it requires a very sophisticated technique of patterning the metal film into wiring of the group of electrode terminals 103 (process in which the metal film is etched by dry etching to the interface between the glass substrate 101 and the metal film but without reaching the interface, and then removing the remaining metal film by wet etching without damaging the interface in the light receiving area of the glass substrate 101.
It is an object of the present invention to inexpensively provide a high-quality solid-state imaging device and a manufacturing method thereof by way of preventing adhesion of foreign objects on a light receiving surface.
In order to achieve this object, a manufacturing method of a solid-state imaging device of the present invention includes the steps of forming an insulating layer on a transparent substrate (insulating layer forming step); forming a wiring layer having a predetermined pattern on the insulating layer (wiring layer forming step); uncovering a surface of a light receiving area of the transparent substrate after forming the wiring layer by removing a portion of the insulating layer formed in the insulating layer forming step corresponding to a light receiving area of a solid-state imaging element (insulating layer removing step); and bonding the solid-state imaging element with the wiring layer so as to mount the solid-state imaging element on the transparent substrate (bonding step).
According to this method, the light receiving surface of the transparent substrate is covered with the insulating layer in the insulating layer forming step, and the light receiving surface of the transparent substrate is protected by the insulating layer during handling and operation in the subsequent wiring layer forming step. Further, in the insulating layer removing step immediately before the step of bonding the solid-state imaging element with the transparent substrate, a portion of the insulating layer corresponding to the light receiving area of the solid-state imaging element is removed so as to uncover the surface of the light receiving area of the transparent substrate.
As a result, foreign objects which might have stuck to the portion of the insulating layer corresponding to the light receiving area of the solid-state imaging element in the wiring layer forming step are removed together with the insulating layer in the subsequent insulating layer removing step. Therefore, with the foregoing manufacturing method, operations which might pose the risk of sticking foreign objects during the manufacturing process can be eliminated as much as possible to realize a manufacturing process of high productivity, thereby inexpensively providing a high-quality solid-state imaging device for products which incorporate solid-state imaging devices, for which demand for reducing the size and thickness has not been higher.
Further, the wiring layer formed in the wiring forming step is formed on the transparent substrate via the insulating layer which is formed in the insulating layer forming step, instead of directly forming it on the transparent substrate. Thus, it is possible to easily carry out patterning without damaging the surface of the light receiving area of the transparent substrate in patterning of wiring of the wiring layer, thus obtaining desirable adhesion between the transparent substrate and the wiring layer.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.